22 



REPORT 1869. 



vage fissures, cand the prism consequently became incapable of being worked. As 

 this was probably due to internal strains analogous to those in imannealed glass, 

 which were fm-ther rendered evident by a considerable action on the polarized 

 ray, inconsistent with the normal character of the crystal, it occurred to the 

 author that this inconvenience might probably be remedied by some process 

 of annealing ; and the result proved to be completely successful. Owing to the 

 low heat-conductibility of rock-salt, and its great lial)ility to fissure on change of 

 temperature, it was obviously necessary that that change should be effected veiy 

 slowly. With this view the rock-f;alt was deeply imbedded in sand in a tin box, 

 and gi-adually during twelve hours heated up to about 250^ C. by a flame of gas 

 placed beneath; it was then allowed to cool gradually, and was subsequently 

 woi-ked without any difficult)'. It further appeared that the previously observed 

 action on polarized light was very sensibly di.ainished, as was sliown by comparing- 

 two sketches make by Mr. Erowning before and after the process of annealing. 



On the lielation between the Specific Refractive Enenjies and the Comhininxj 

 Proportions of Metals. Bij J. H. Gladstone, Ph.D., F.R.S. 



Tlie specific refractive energies of thirty metals had been determined by the 

 author mainly from aqueous solutions of their salts. These metals were aiTanged 

 in the order of their energies, and against them were placed their combining pro- 

 portions, — that is, the actual amount of the metal which forms a stable salt, when 

 combined ^^'itll an equivalent of some other body, such as .3-3 'S of chlorine. 



It will be seen tliat while the number.? of the first column decrease, those of the 



